1. Field of Invention
This invention relates to a coated abrasive article and to a method of making such an article.
2. Discussion of the Art
Coated abrasive articles generally comprise a flexible backing to which is adhered a coating of abrasive grits. The coated abrasive article typically employs a "make coat" of resinous adhesive material in order to secure or bond the abrasive grits to the backing and a "size coat" of resinous material applied over the make coat and abrasive grits in order to firmly bond the abrasive grits to the backing.
The flexible backing can be made of cloth, paper, polymeric film, nonwoven materials, vulcanized fiber, and combinations thereof. Cloth is widely used as a coated abrasive backing on account of its strength, heat resistance, and flexibility. However, cloth backings have some major disadvantages. Cloth backings are generally more expensive than other types of backings. Additionally, because cloth backings are generally porous, they have to be sealed or treated, thereby significantly adding to their cost. If the cloth backing is not sealed, the make coat will penetrate into the interstices of the cloth, resulting in a deficiency of binder, and the subsequently applied abrasive grits will not adhere to the backing. The cloth backing is typically sealed by one or more treatment coats, such as a saturant coat, a presize coat, a backsize coat, or a subsize coat. A saturant coat saturates the cloth, resulting in a stiffer cloth with more body. An increase in body provides an increase in strength and durability of the article. A presize coat, which is applied to the front side of the backing, may add bulk to the cloth or may improve adhesion of subsequent coatings. A presize coat also protects the yarns of the cloth. A presize coat is extremely useful for coated abrasive articles utilizing fine grades of abrasive grits. A backsize coat, which is applied to the back side of the backing, i.e., the side opposite to which the abrasive grits are applied, adds body to the backing and protects the yarns of the cloth from wear. A subsize coat is similar to a saturation coat except that it is applied to a previously treated backing.
These treatment coats typically comprise thermally curable resinous adhesives, such as phenolic resins, epoxy resins, acrylate resins, acrylic latices, latices, urethane resins, glue, starch and combinations thereof.
U.S. Pat. No. 2,712,987 discloses a coated abrasive having a nylon substrate. The nylon softened and then the abrasive grits are applied. The nylon serves both as the backing and as the make coat.
U.S. Pat. No. 3,230,672 discloses a coated abrasive in which the abrasive grits have been forced into the make coat such that the height of the abrasive grits is essentially the same.
U.S. Pat. No. 4,163,647 discloses a method of making a cloth backed coated abrasive in which the cloth is coated on its front side with a liquid thermosetting resin in such a manner that the thermosetting resin does not permeate the interstices of the cloth.
A utility cloth having the tradename of "VORAX" has a make coat that does not penetrate the interstices of the cloth. The make coat is selected from the group consisting of glue, phenolic resins, latices, or phenolic resins/latices.
In recent years radiation curable resins have been proposed as cloth treatments or binders for coated abrasives as a substitute for conventional thermally curable resins. Radiation curable resins can be cured much more rapidly than can phenolic resins. If additional heat is provided in an attempt to more rapidly cure phenolic resins, the viscosity of the phenolic resin will decrease, thereby resulting in bleeding of the resin through the backing. As a result of this bleed through, the backing hardens and loses flexibility.
U.S. Pat. Nos. 4,047,903; 4,588,419; 4,927,431; 4,903,440 disclose abrasive articles comprising abrasive grits and a binder formed from a radiation curable resin.